A new technique has been developed for isolating 100% of the DNA of phage lambda from an infected E. coli. Samples can easily be taken at one minute intervals after infection and rapidly prepared for electron microscopic observation. We are examining these molecules in an effort to determine when replication begins, what fraction of the pool of molecules are replicating at any particular time, whether there is a time interval between rounds of replication, when rolling circle replication bounds, and whether there are any novel structures within the cell. The timing of recombination and the structure of recombinational intermediates will also be determined.